Subclinical necrotizing enterocolitis-induced systemic immune suppression in neonatal preterm pigs

Abstract

Preterm infants are at high risks of sepsis and necrotizing enterocolitis (NEC). Some develop sepsis shortly after suspected or confirmed NEC, implying that NEC may predispose to sepsis but the underlying mechanisms are unknown. Using NEC-sensitive preterm pigs as models, we investigated the immune status in animals following development of sub-clinical NEC-like lesions with variable severities. Caesarean-delivered preterm pigs were reared until day 5 or 9. Blood was analyzed for T cell subsets, neutrophil phagocytosis, transcriptomics and immune responses to in vitro LPS challenge. Gut tissues were used for histology and cytokine analyses. Pigs with/without macroscopic NEC lesions were scored as healthy, mild or severe NEC. Overall NEC incidence was similar on days 5 and 9 (61-62%) but with lower severity on day 9, implying gradual mucosal repair following the early phase of NEC. Pigs with NEC showed decreased goblet cell density and increased MPO+ and CD3+ cell infiltration in the distal small intestine or colon. Mild or severe NEC lesions had limited effects on circulating parameters on day 5. On day 9, pigs with NEC lesions (especially severe lesions) showed systemic immune suppression, as indicated by elevated Treg frequency, impaired neutrophil phagocytosis, low expression of genes related to innate immunity and Th1 polarization, and diminished LPS-induced immune responses. In conclusion, we shows evidence for NEC-induced systemic immune suppression, even with mild and sub-clinical NEC lesions. The results help to explain that preterm infants suffering from NEC may show high sensitivity to later secondary infections and sepsis.

Neonatal intestinal mucus barrier changes in response to maturity, inflammation, and sodium decanoate supplementation

“…In contrast to the healthy preterm piglets, the preterm piglets that developed NEC showed a different pattern. In these NEC piglets, the mucus barrier was unable to trap and confine the NPs (large pathogen model compound), which was consistent with higher levels of bacteria adhering to the NEC intestinal mucosa and increased expression levels of innate inflammatory cytokines ( IL6 and IL8 ), as previously reported 34 , 45 . However, we did not observe any significant differences in goblet cell density or gene expression of the predominantly intestinal gel-forming mucin, MUC2 , in the NEC piglets.…”

“…This suggests that the amount of mucins does not differ in the NEC condition and that other factors such as mucus composition and mucin PTM structure may regulate the mucus barrier instead. Although the NEC condition in our preterm piglets corresponds to a more sub-clinical NEC condition than in human infants 34 , we found that the mucus barrier was significantly impaired by this sub-clinical NEC state. This indicates that the mucus barrier may be an important factor in the NEC condition.…”

“…We next sought to investigate how the properties of mucus and mucosa are affected in piglets with impaired health conditions known to negatively affect postnatal gut development, namely PA and NEC 6 , 7 , 9 . In the case of near-term piglets with PA, we specifically sampled small intestines that were macroscopically evaluated as "healthy" (with a score of 1–2 34 , 35 ) to examine whether the PA condition altered the mucus properties. This analysis aimed to provide insights into why infants with PA may have a higher risk of developing NEC 9 , 10 .…”

“…This analysis aimed to provide insights into why infants with PA may have a higher risk of developing NEC 9 , 10 . For preterm piglets with NEC, impaired small intestines (with a macroscopic NEC score of 3–6 34 , 35 ) were collected. Representative images of both healthy and NEC-impaired intestinal mucus and mucosa are shown in Fig.…”

Editorial: Immunity in Compromised Newborns

“…On this background, it is not surprising that 10-30% of very preterm infants develop immune-related disorders such as NEC and LOS and that many organ complications in preterm infants are partly related to dysregulated local host immune responses to infection/ inflammation. Hyper-inflammatory conditions like NEC and LOS may also induce immunosuppression, predisposing to secondary infection risks, as indicated by infant studies (16) and blood cell transcriptome and immune studies in preterm pigs with NEC (17,18).…”